The present invention relates generally to tire retreading envelopes and more specifically it relates to a two-piece retread envelope having three points at which it forms a seal around the tire.
It is conventional in retreading to use a one-piece annular retread envelope having a U-shaped cross-section that seals at two points. Examples of U-shaped annular retread envelopes are described in detail in U.S. Pat. Nos. 5,346,378; 4,836,877; 4,036,271; 4,634,357; and 5,518,384. These references disclose various concepts of manufacturing and uses of U-shaped radial design retread envelopes.
Worn tread on a used tire casing is buffed off to a profile suitable for mounting a new tread. Then, a pre-cured and buffed tread is adhered about the periphery of the casing with a laminate of uncured cushion gum cemented between the tread and the casing. An outer annular elastomeric curing envelope having an inwardly-opening U-shaped radial cross-section is positioned over the new tread and a portion of the outer sidewall of the tire casing. A pair of annular elastomeric sealing rings are secured about the inner peripheral beads of the tire casing and cooperate with the outer curing envelope to enclose the tire casing outer sidewalls. A vacuum is drawn through a valve in the outer curing envelope for stretching the envelope into intimate contact with all surfaces of the tread. The tire is then placed in an autoclave for several hours at an elevated temperature and pressure to cure the gum and positively bond the casing and tread. The outer curing envelope and sealing rings are removed and the retreaded tire is ready for use. Thus, retreading envelopes have been used for years and typically they are composed of a compound material that is heat resistant and molded in an annular configuration which covers all three surfaces of the tire, namely the peripheral tread and the two opposing sidewalls.
The main problem with conventional retread envelopes is premature failure during this process of enveloping the tire. The U-shaped cross-section retread envelope requires the envelope to be stretched over the tire being retreaded. The process of enveloping the tire using this design can require the compound to elongate as much as (700%) seven hundred percent. This extreme elongation causes the retread envelope to either tear or lose its elastic quality, which is known in the industry as xe2x80x9cbagging out.xe2x80x9d Another problem with conventional retread envelopes is the extreme elongation to envelope the tire which is achieved by formulating the compound to be polymer rich making it expensive to manufacture. Compounds formulated to be polymer rich rather than carbon rich and elongate as much as (700%) seven hundred percent do not heat-age well which makes them expensive to use. Another problem with conventional tire retreading is the level of difficulty for the end user during the process of enveloping the tire due to its U-shaped cross-section.
While these devices may be suitable for the particular purpose to which they address, they are not as suitable for the process of curing precure tread to a tire casing as the present invention which meets the need for a more durable, cost-effective, and safer retread envelope system. The general purpose of the present invention, which will be described subsequently in greater detail, is to provide a new two-piece retread envelope that has many of the advantages mentioned heretofore and many novel features that result in a new two-piece retread envelope which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art, either alone or in any combination thereof.
In view of the foregoing disadvantages inherent in the known types of retread envelopes now present in the prior art, the present invention provides a new two-piece retread envelope wherein the same can be utilized for curing precure tread to a tire casing to provide a more durable, cost effective, and safer-to-use envelope. This is achieved by a two-piece retread envelope having three points at which it forms a seal around the tire. A first sealing point is located at the sealing bead of the tire. A second sealing point is the bead area on the opposite side of the tire. A third sealing point is located along a seam between the two envelope parts near the outside diameter of the tire.
It is therefore the primary objective of the present invention to provide a two-piece retread envelope which will overcome the shortcomings of the prior art devices.
Another objective of the present invention is to provide a two-piece retread envelope for curing precure tread to a tire casing to provide a more durable, cost effective, and safer-to-use envelope.
Yet another objective is to provide a two-piece retread envelope which is more cost effective for the end user. This is achieved by employing a two-piece design retread envelope, which has a minimal need for elongation. Tearing of envelopes is virtually eliminated. This design allows the compound to be formulated carbon rich rather than polymer rich reducing the material and manufacturing cost. The carbon rich formulation improves longevity and eliminates bagging out.
Another objective is to provide a two-piece retread envelope which is safer and easier for and easier to manufacture. Yet another objective is to provide a two-piece retread envelope which is more versatile and requires less inventory.
To achieve these objectives, a partial envelope providing an annular cavity and having a J-shaped cross-section together with a radial sidewall closure having a Z-shaped cross-section are employed. Both are molded from a heat resistant compound. The two-piece envelope requires minimal need for elongation making it effortless to mount and dismount from the mold during the manufacturing process.
More specifically, the applicant has invented a retread autoclave vacuum envelope for a vehicle tire casing comprising a first portion of a two-part retread vacuum envelope having a generally J-shaped cross-section providing an annular cavity for receiving a first sidewall and the peripheral tread of a tire assembly. The tire assembly comprises a tire casing, an encircling pre-cured tread, and an intermediate layer of adhesive affixing a crown of the casing to the tread. The first portion is a unitary element providing scalable contact against a first sidewall of the tire casing and extending radially outwardly along a first sidewall from a bead area of the tire casing, then laterally across the outer surface of the tread and extending beyond a far shoulder of the tire assembly to an annular seal lip. A second portion of the envelope being a unitary annular closure lies along a second tire casing sidewall, the closure including a sealed joint against the first envelope portion. The joint has contact surface areas on an inside surface of the lip of the first envelope portion adjacent the far shoulder of the tire assembly and a surface area on an outer rim of the closure. The closure has a generally Z-shaped cross-section comprising a reinforced edge along its outer diameter, a generally laterally-extending outer rim, a radially inward extending skirt portion, and an inner rim adjacent an inside diameter of the closure molded to form fit a bead of the tire casing. The sidewall closure further includes a reinforced edge along an innermost surface thereof. The outer diameter of the tire assembly is greater than the inner diameter of the first portion of the envelope in a crown area thereof, the first portion extending from a near side of the tread across and beyond the far shoulder of the tire assembly to the annular lip in a sealing area of the joint. The sidewall closure is composed of the semi-rigid material dimensioned such that the outermost diameter of the sidewall closure is greater than the inner diameter of the lip of the first envelope portion, thereby causing an interference fit therebetween. The envelope further includes a radially expanding sealing ring mounted against the bead area of the tire casing, the ring forceably pressing the inner rim of the closure against the bead area of the tire casing. A valve restricts the flow of air through a port located through the surface of the first envelope portion. The first envelope portion and the closure are both composed of a heat resistant compound. The seal lip projects laterally away from the second tire casing sidewall. An alternate embodiment is further described in that the lip extends partway along an upper portion of the second tire sidewall. In yet another embodiment, a first J-shaped envelope is in sealed contact with a second closure envelope along a peripheral seam which is adjacent the crown area of the tire tread.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter. In these respects, the two-piece retread envelope according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides an apparatus primarily developed to be more durable, cost effective and safer to use.
To the accomplishment of the above and related objectives, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated. Various other objectives, features and attendant advantages of the present invention will become fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views